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    <title>Remove Comments</title>
    <link rel="stylesheet" href="doc.css">
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<h1>Remove Comments</h1>

<h2>Configuration</h2>
<p>
The 'Remove Comments' filter is enabled by specifying:
<dl>
  <dt>Apache:<dd><pre class="prettyprint"
     >ModPagespeedEnableFilters remove_comments</pre>
  <dt>Nginx:<dd><pre class="prettyprint"
     >pagespeed EnableFilters remove_comments;</pre>
</dl>
<p>
in the configuration file.  To retain comments that have semantic reason to be
delivered to the browser, you may specify one more wildcard patterns
using <code>RetainComment</code> directives.  For example:
<dl>
  <dt>Apache:<dd><pre class="prettyprint"
     >ModPagespeedRetainComment " google_ad_section*"</pre>
  <dt>Nginx:<dd><pre class="prettyprint"
     >pagespeed RetainComment " google_ad_section*";</pre>
</dl>
</p>

<h2>Description</h2>
<p>
The <code>remove_comments</code> filter eliminates HTML comments,
which are often used to document the code or to comment out
experiments.  Note that this directive applies only to HTML files.
CSS comments are eliminated with the
<code>rewrite_css</code> filter, and Javascript comments are
eliminated with the <code>rewrite_javascript</code> filter.
</p>
<p>
The filter reduces the transfer size of HTML files by removing most HTML
comments. Depending on the HTML file, this filter can significantly reduce the
number of bytes transmitted on the network.  Also note that
the <code>RetainComment</code> directive currently only applies to HTML files --
the wildcard pattern is not currently used for retaining CSS or Javascript
comments.
</p>
<p>
For example, if the HTML document looks like this:
</p>
<pre class="prettyprint">
&lt;html&gt;
&lt;body&gt;
&lt;!-- Display the site logo here --&gt;
&lt;img src="logo.png"&gt;
&lt;!-- Now show the page contents --&gt;
&lt;div&gt;Some content here&lt;/div&gt;
&lt;!-- Apply IE-specific CSS --&gt;
&lt;!-- [if IE ]&gt;
&lt;link href="iecss.css" rel="stylesheet" type="text/css"&gt;
&lt;![endif]--&gt;
&lt;!-- google_ad_section_end  -- retained due to RetainComment directive --&gt;
&lt;/body&gt;
&lt;/html&gt;
</pre>
<p>
Then PageSpeed, with the above directives specified, will rewrite it into:
</p>
<pre class="prettyprint">
&lt;html&gt;
&lt;body&gt;
&lt;img src="logo.png"&gt;
&lt;div&gt;Some content here&lt;/div&gt;
&lt;!-- [if IE ]&gt;
&lt;link href="iecss.css" rel="stylesheet" type="text/css"&gt;
&lt;![endif]--&gt;
&lt;!-- google_ad_section_end  -- retained due to RetainComment directive --&gt;
&lt;/body&gt;
&lt;/html&gt;
</pre>
<h3>Example</h3>
<p>
You can see the filter in action at <code>www.modpagespeed.com</code> on this
<a href="https://www.modpagespeed.com/examples/remove_comments.html?ModPagespeed=on&amp;ModPagespeedFilters=remove_comments">example</a>.
</p>

<h2>Notes</h2>
<p>
The "Remove Comments" filter is aware of
<a href="http://msdn.microsoft.com/en-us/library/ms537512(VS.85).aspx">Internet Explorer conditional comments</a> and does not remove them.
</p>

<h2>Risks</h2>
<p>
This filter is low risk for most web pages. Some web pages use comments to
embed data or JavaScript, in order to reduce the parse time of the HTML
document. Such pages sould disable this filter, as it will remove the
comments containing the data or JavaScript that is needed by these web
pages.
</p>


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